1. FIELD OF THE INVENTION
The invention relates to a powder-filled steel tube in coiled form, having a tube wall with a welded longitudinal seam and which is wound into a coil and to a method of continuous manufacture of such a tube.
2. DESCRIPTION OF THE PRIOR ART
European patent publication 0003370 illustrates a tube of the kind described above and a method of its manufacture. This product can be used in steel making for alloying liquid steel or for adding oxidizing agents into a steel ladle. It is therefore known as "ladle wire". This ladle wire, with a typical diameter of 5 to 18 mm, is injected vertically into the liquid steel bath at a speed of between 1 to 10 meters per second.
At present this ladle wire is supplied in parallel wound coils. "Parallel wound" means a coil in which the different windings of wire are wound layer-wise next to each other and against each other. In order to uncoil the wire without twisting it, it is necessary to set up such a coil so that it revolves around its axis whereby the wire is pulled off from the coil by the injection device. However, some users find it troublesome to set up such a coil rotatably and they prefer to place the coil on the floor and draw off the wire end starting from the innermost layer. Clearly this means that the wire becomes twisted.
In practice, this twisting can impose so much stress on the seam of the welded steel tube that the ladle wire ruptures at the seam and part of the powder spills out.